The life processes cannot continue in the body cells without sources of energy. From glucose, energy is released to produce ATP, the driving force of the life processes of the body.
a. When a specific portion of the cerebral cortex is active, more blood is delivered to that portion. This is an example of how more blood can be delivered to the body parts where it is most needed.
b. When the hormone epinephrine (Adrenalin) is secreted by the adrenal gland, it is delivered to all parts of the body by the cardiovascular system. Among other effects, epinephrine increases the rate of metabolism of all cells of the body. This helps to mobilize energy during a "fight-or-flight" stress reaction.
c. In periods when much energy is required, the body can use its stores of fat as a source of energy. As we have seen in the chapter on the digestive system, the lymphatic circulatory system picks up the end products of lipid (fat) digestion and carries them to the cardiovascular system.
(1) This fat is generally deposited throughout the body, particularly the subcutaneous layer, as yellow fat. In a rapid turnover, the high energy content of the fat is released for use throughout the body.
(2) In infants, there is often brown fat at the junctions of the major blood vessels. In periods of high-energy requirements, this brown fat releases energy into the blood stream immediately.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.